We have prepared inert model solid rocket propellants of two kinds, polycaprolactone (PCP) networks highly (60%) plasticized with triacetin and hydroxyl-terminated polybutadiene (HTPB) cross-linked with isophorone diisocyanate, both filled with over 65% NaSO4 and Al powders as well as traces of fine carbon fibrils 100 Angstrom thick and several micrometers long. Sheets of these dielectric composites were used for de surface and volume electrical resistivities near room temperature. Addition of less than 1% fibrils in the PCP composites reduces volume resistivity by a factor of 10. The amount required for HTPB is only 0.1%, leaving processability unaffected; resistivity reduction rises from one to nearly four orders of magnitude as potential difference is increased from 10 to 500 V. Addition of fibrils to HTPB composites is a promising candidate for minimizing the incidence of dangerous electric discharge events.